Cathodic protection in which a potential of a steel material such as a reinforcing bar in concrete is dropped to a potential at which corrosion does not occur by flowing a current through the steel material from an electrode (anode) installed near a surface of the concrete to inhibit progress of corrosion of the steel material is known. An external power supply method and a galvanic anode are known for such cathodic protection.
The external power supply method is anode corrosion protection in which a positive electrode of a direct current power supply is connected to a corrosion protection anode via a conductor and a negative electrode of the direct current power supply is connected to a steel material of an object to be protected from corrosion via a conductor to form an electric circuit so that a corrosion protection current flows through the electric circuit from the corrosion protection anode to the steel material.
In the external power supply method, a corrosion protection anode with high corrosion resistance such as titanium mesh, a titanium grid, and a titanium rod is installed at a surface of concrete directly or through a groove or a hole provided at the surface and is fixed with mortar. In this aspect, there are problems in that it is disadvantageous in terms of the cost due to the high price of the anode with high corrosion resistance and the construction thereof requires a significant amount of labor.
Meanwhile, a method in which platinum-coated titanium lines are installed at predetermined intervals on a concrete surface and the whole concrete surface is coated with a conductive coating material is being developed. However, in this method, potential distribution becomes non-uniform according to a state of a contact surface between the conductive coating film and the concrete, and thus there is a problem in that the conductive coating film is prone to degradation and separation due to an electrochemical reaction.
With respect to the problems above, in Japanese Unexamined Patent Application, First Publication No. 2004-190119, a corrosion protection method in which a carbon fiber sheet coated with an oxidation-resistant metal having a passive film is used for reinforcing a concrete structure, and a filling material layer of a cement base that includes a passive protectant for inhibiting breakdown of the passive film and an electrolyte is provided on a surface of the concrete structure so that conduction occurs at the carbon fiber sheet is proposed.
However, in this method, a masking tape is attached and an adhesive is applied in a stripe pattern to a spot at which the filling material layer will be installed on the surface of the concrete structure. Then, the masking tape is peeled off, and the carbon fiber sheet is attached. After the carbon fiber sheet is attached, two tubular bodies are made to pass through the spot at which the filling material layer will be installed such that air is discharged through one of the two tubular bodies and the filling material is injected between the carbon fiber sheet and the surface of the concrete structure through the other of the two tubular bodies. Then, an impregnating adhesive is impregnated from an upper portion of the carbon fiber sheet.
In this case, the work of providing the adhesive layer and the filling material layer in the stripe pattern becomes laborious because the work is required to be performed overhead at a site of the corrosion protection work in which a treatment is performed at a back surface of a structure such as a floor slab of a bridge in many cases.
To lighten anode installation work at a site, in PCT International Publication No. 2013/031663 WO, a supplementary anode is proposed. In the supplementary anode, an electrolyte layer formed in a sheet shape and having adhesive power such that the electrolyte layer is capable of adhering to the conductive layer and to the surface layer of the object to be protected from corrosion is adhered to one surface of the conductive layer on which a carbon material is formed in a sheet shape.
In the proposal of PCT International Publication No. 2013/031663 WO, the anode is manufactured in a factory, and the carbon material formed in a sheet shape is only adhered to the electrolyte layer on the surface of the concrete to install the anode at the site. Because of this, it is very easy to install an anode.
In addition, since the electrolyte is adhered to the whole concrete surface of a portion targeted for corrosion protection, a charge transfer is very efficiently performed compared to a case in which the filling material layer of the cement base is provided in the stripe pattern. Also, since an anode surface is not coated with an oxidation-resistant metal, it is advantageous in terms of the cost, and breakdown of a passive film does not occur.